This invention relates generally to fire protection systems and, more particularly, to fire protection systems in which a plurality of individual fire suppressor units are activated to extinguish a fire.
Certain fire protection systems employ a plurality of strategically located suppressor units, each including a vessel filled with a fire suppressing agent and an electrically operated release mechanism for inducing discharge of the agent in response to detection of a fire. When simultaneous operation of all suppressor units is desired, the system is provided typically with a control circuit that produces coincident activation of all release mechanisms. In such systems, it is common technique to electrically supervise the electric integrity of the release mechanisms by providing and monitoring a trickle current through a series connection thereof. Although this series supervision establishes a constant knowledge of release mechanism integrity, there remains the possibility that a single release member failure will cause failure of the entire series system. In addition, even a detected failure of a release mechanism can prevent system operation if the detected failure occurs coincidentally with a demand for system actuation.
A fire protection system directed toward solving these problems is described in U.S. Pat. No. 3,917,001. The system disclosed in that patent responds to the detection of a fire by initially establishing in a conventional manner, a flow of activating current through the suppressing agent release mechanisms which are connected in a series. However, after this initial stage of operation, a control circuit reconnects the release mechanisms in parallel across a power supply. Because of this series to parallel circuit transformation, the failure of a single release mechanism will not prevent activation of all other mechanisms during the parallel mode of operation. Although obviating many problems associated with series connected suppressor units, this system also exhibits certain disadvantages when used in applications requiring a large number of suppressor units. For example, the activation of a large number of suppressors connected in a parallel mode requires a large capacity power source capable of supplying the cumulative current requirements of all units. In addition, the series to parallel conversion requires that each suppressor unit be connected to a central control with two wires and requires a large number of relays for effecting the transformation. These factors add to the cost of the system while reducing its reliability.
The object of this invention, therefore, is to provide a more reliable, less costly fire protection system of the type employing a large number of individual suppressor units, all having electrically operated release mechanisms adapted for sympathetic activation.